There are two types of "bug" that you will commonly see on glass of an aquarium. There is something called cyclops which is a small species of copepod, the females carry two eggs near the base of their tail which make them appear to look like a small white "Y" the other is a small flat worm called planaria, both of them are harmless. The best way to rid yourself of them is frequent water changes along with less feeding, they frequent aquariums where over feeding is constantly occuring. Someone also mentioned filter maintenance which is also a very good method.